1. Field of the Invention
The present invention relates to a planar dielectric line for use in a microwave or a millimeter-wave band. The invention also relates to an integrated circuit using the dielectric line.
2. Description of the Related Art
Microwaves and millimeter-waves, which are electromagnetic waves in a very wide frequency band ranging from 300 MHz to 300 GHz, are used in various types of radar, terrestrial long-distance telephone transmission, television broadcasting relays, satellite communications, etc. Such waves are also coming into a wide use in the field of mobile communications. Meanwhile, research is being actively carried out in the development of MMICs, and progress is being made in the downsizing of equipment utilizing electromagnetic waves in a band including microwaves and millimeter-waves. Accordingly, the microwaves and millimeter-waves are increasingly coming into a wider range of uses.
Hitherto, the following type of transmission lines have been largely used in this band range of microwave and millimeter-waves: transmission lines, such as waveguides, coaxial lines, microstrip lines, coplanar lines, slotted lines, and so on. These types of lines are constructed by forming predetermined electrodes on a dielectric substrate. Waveguides are for use in portions where conduction losses should be inhibited to a low level. Coaxial lines are widely used as connecting cables between equipment. Also, microstrip lines, slotted lines, etc. are largely employed for the connection between electronic parts, such as ICs, since they are easily connected thereto.
A slotted line is, as shown in FIG. 19, constructed in such a manner that electrodes 421a and 421b are disposed across a predetermined spacing on the top surface of a dielectric substrate 423 having a predetermined thickness h400. This achieves the formation of a slot 424 having a predetermined width W400 sandwiched between the electrodes 421a and 421b. In the slotted line constructed as described above, an electromagnetic wave forms a mode having an electric field E400 in parallel to the width of the slot 424 and a magnetic field H400 in parallel to the longitudinal direction of the slot 424, thereby propagating in the longitudinal direction of the slot 424.
Further, in addition to the above-described transmission lines, nonradiative dielectric waveguides (NRD) are used. An NRD is constructed in such a manner that a rectangular-prism dielectric is interposed between conductive plates and has a low level of conduction losses.
Waveguides, which are of large size, cannot however achieve downsizing and weight reduction and are difficult to connect with electronic parts, such as ICs. On the other hand, in coaxial lines, an unnecessary high-order mode is generated at a frequency higher than a specific frequency determined by the cross sectional configuration of the coaxial lines so as to increase conduction losses, thus rendering the lines inoperable. In order to avoid this problem, it is necessary to reduce the diameter of the coaxial line to approximately 1 mm when the line is used at a frequency in a millimeter-wave band range of as high as 60 GHz, which makes it difficult to manufacture. Microstrip lines, coplanar lines and slotted lines exhibit extremely large conduction losses. Additionally, NRD lines are difficult to connect to electronic parts, such as ICs.